Dual 18-Bit Audio DAC
Dual Serial Input, Voltage Output DACs
Single +5 V Supply
0.004% THD+N (typ)
Low Power: 50 mW (typ)
108 dB Channel Separation (min)
Operates at 8؋ Oversampling
16-Pin Plastic DIP or SOIC Package
Portable Compact Disc Players
Portable DAT Players and Recorders
Automotive Compact Disc Players
Automotive DAT Players
The AD1868 is a complete dual 18-bit DAC offering excellent
performance while requiring a single +5 V power supply. It is
fabricated on Analog Devices’ ABCMOS wafer fabrication pro-
cess. The monolithic chip includes CMOS logic elements, bipo-
lar and MOS linear elements, and laser-trimmed thin-film
resistor elements. Careful design and layout techniques have re-
sulted in low distortion, low noise, high channel separation, and
low power dissipation.
The DACs on the AD1868 chip employ a partially segmented
architecture. The first three MSBs of each DAC are segmented
into seven elements. The 15 LSBs are produced using standard
R-2R techniques. The segments and R-2R resistors are laser
trimmed to provide extremely low total harmonic distortion.
The AD1868 requires no deglitcher or trimming circuitry. Low
noise is achieved through the use of two noise-reduction capacitors.
Each DAC is equipped with a high performance output ampli-
fier. These amplifiers achieve fast settling and high slew rate,
producing ± 1 V signals at load currents up to ± 1 mA. The
buffered output signal range is 1.5 V to 3.5 V. Reference volt-
ages of 2.5 V are provided, eliminating the need for “False
A versatile digital interface allows the AD1868 to be directly
connected to all digital filter chips. Fast CMOS logic elements
allow for an input clock rate of up to 13.5 MHz. This allows for
operation at 2×, 4×, 8×, or 16× the sampling frequency for each
channel. The digital input pins of the AD1868 are TTL and
+5 V CMOS compatible.
*Protected by U.S. Patent Numbers: 3,961,326; 4,141,004; 4,349,811;
4,857,862; and patents pending.
FUNCTIONAL BLOCK DIAGRAM
The AD1868 operates on +5 V power supplies. The digital sup-
ply, VL, can be separated from the analog supply, VS, for re-
duced digital feedthrough. Separate analog and digital ground
pins are also provided. In systems employing a single +5 volt
power supply, VL and VS should be connected together. In bat-
tery operated systems, operation will continue even with reduced
supply voltage. Typically, the AD1868 dissipates 50 mW.
The AD1868 is packaged in either a 16-pin plastic DIP or a 16-
pin plastic SOIC package. Operation is guaranteed over the tem-
perature range of –35°C to +85°C and over the voltage supply
range of 4.75 V to 5.25 V.
1. Single-supply operation @ +5 V.
2. 50 mW power dissipation (typical).
3. THD+N is 0.004% (typical).
4. Signal-to-Noise Ratio is 97.5 dB (typical).
5. 108 dB channel separation (minimum).
6. Compatible with all digital filter chips.
7. 16-pin DIP and 16-pin SOIC packages.
8. No deglitcher required.
9. No external adjustments required.
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
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